[flang] AliasAnalysis: Handle fir.load on fir.alloca (llvm#117785)

For example, determine that the address in p below cannot alias the
address of v:

```
subroutine test()
  real, pointer :: p
  real, target :: t
  real :: v
  p => t
  v = p
end subroutine test
```

Author: jdenny-ornl

flang/lib/Optimizer/Analysis/AliasAnalysis.cpp

@@ -51,14 +51,22 @@ static bool hasGlobalOpTargetAttr(mlir::Value v, fir::AddrOfOp op) {
       v, fir::GlobalOp::getTargetAttrName(globalOpName));
 }
 
-static mlir::Value getOriginalDef(mlir::Value v) {
+static mlir::Value
+getOriginalDef(mlir::Value v,
+               fir::AliasAnalysis::Source::Attributes &attributes,
+               bool &isCapturedInInternalProcedure) {
   mlir::Operation *defOp;
   bool breakFromLoop = false;
   while (!breakFromLoop && (defOp = v.getDefiningOp())) {
     llvm::TypeSwitch<Operation *>(defOp)
         .Case<fir::ConvertOp>([&](fir::ConvertOp op) { v = op.getValue(); })
-        .Case<fir::DeclareOp, hlfir::DeclareOp>(
-            [&](auto op) { v = op.getMemref(); })
+        .Case<fir::DeclareOp, hlfir::DeclareOp>([&](auto op) {
+          v = op.getMemref();
+          auto varIf = llvm::cast<fir::FortranVariableOpInterface>(defOp);
+          attributes |= getAttrsFromVariable(varIf);
+          isCapturedInInternalProcedure |=
+              varIf.isCapturedInInternalProcedure();
+        })
         .Default([&](auto op) { breakFromLoop = true; });
   }
   return v;
@@ -600,7 +608,8 @@ AliasAnalysis::Source AliasAnalysis::getSource(mlir::Value v,
             if (mlir::isa<fir::PointerType>(boxTy.getEleTy()))
               attributes.set(Attribute::Pointer);
 
-            auto def = getOriginalDef(op.getMemref());
+            auto def = getOriginalDef(op.getMemref(), attributes,
+                                      isCapturedInInternalProcedure);
             if (auto addrOfOp = def.template getDefiningOp<fir::AddrOfOp>()) {
               global = addrOfOp.getSymbol();
 
@@ -609,13 +618,13 @@ AliasAnalysis::Source AliasAnalysis::getSource(mlir::Value v,
 
               type = SourceKind::Global;
             }
-
-            // TODO: Add support to fir.alloca and fir.allocmem
-            // if (auto allocOp = def.template getDefiningOp<fir::AllocaOp>()) {
-            //   ...
-            // }
-
-            if (isDummyArgument(def)) {
+            // TODO: Add support to fir.allocmem
+            else if (auto allocOp =
+                         def.template getDefiningOp<fir::AllocaOp>()) {
+              v = def;
+              defOp = v.getDefiningOp();
+              type = SourceKind::Allocate;
+            } else if (isDummyArgument(def)) {
               defOp = nullptr;
               v = def;
             }

flang/test/Analysis/AliasAnalysis/alias-analysis-2.fir

@@ -8,9 +8,11 @@
 // They cannot physically alias
 // CHECK-DAG: p1.addr#0 <-> p2.addr#0: NoAlias
 
-// p1.addr and p2.addr could both be wrapped inside boxes
-// CHECK-DAG: p1.addr#0 <-> boxp1.addr#0: MayAlias
-// CHECK-DAG: p2.addr#0 <-> boxp1.addr#0: MayAlias
+// p1.addr is the address returned by an alloca.  It does not have a target
+// attribute, and it is not the address retrieved from a pointer.  It cannot
+// alias anything.  Likewise for p2.addr.
+// CHECK-DAG: p1.addr#0 <-> boxp1.addr#0: NoAlias
+// CHECK-DAG: p2.addr#0 <-> boxp1.addr#0: NoAlias
 
 // TODO: To really see aliasing, we should be looking at a load of p1.addr
 // p1.addr is just a local address holding the address to the data 
@@ -27,10 +29,11 @@
 // CHECK-DAG: p2.addr#0 <-> func.region0#2: NoAlias
 
 // All arguments are either pointers or targets
-// A pointer in a box may alias with both
+// The address *in* a local pointer may alias the address of a target
+// argument, but it does not alias the address *of* a pointer argument.
 // CHECK-DAG: boxp1.addr#0 <-> func.region0#0: MayAlias
 // CHECK-DAG: boxp1.addr#0 <-> func.region0#1: MayAlias
-// CHECK-DAG: boxp1.addr#0 <-> func.region0#2: MayAlias
+// CHECK-DAG: boxp1.addr#0 <-> func.region0#2: NoAlias
 
 // A target dummy may alias with another target
 // CHECK-DAG: func.region0#0 <-> func.region0#1: MayAlias
@@ -54,7 +57,7 @@
 
 // The addresses stored in two different pointers can alias, even if one has no
 // box.  In this program, they happen to be the same address.
-// T4: 
+// T4 from <https://github.com/llvm/llvm-project/pull/117785#discussion_r1924348480>.
 // CHECK-DAG: p1.tgt#0 <-> boxp1.addr#0: MayAlias
 
 func.func @_QFPtest(%arg0: !fir.ref<f32> {fir.bindc_name = "v1", fir.target}, %arg1: !fir.ref<f32> {fir.bindc_name = "v2", fir.target}, %arg2: !fir.ref<!fir.box<!fir.ptr<f32>>> ) attributes {test.ptr = "func"} {